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前言：

本篇文章主要简介下MySQL中where,group by ,order by ,limit,join,union ,union all,子表等查询语法。

测试数据准备

? 1 2 3 4 5 6 create table emp (  empno numeric(4) not null,  ename varchar(10),  job varchar(9),  mgr numeric(4),  hiredate datetime,  sal numeric(7, 2),  comm numeric(7, 2),  deptno numeric(2)); create table dept (  deptno numeric(2),  dname varchar(14),  loc varchar(13)); create table salgrade (  grade numeric,  losal numeric,  hisal numeric); insert into dept values (10, 'ACCOUNTING', 'NEW YORK');insert into dept values (20, 'RESEARCH', 'DALLAS');insert into dept values (30, 'SALES', 'CHICAGO');insert into dept values (40, 'OPERATIONS', 'BOSTON'); insert into salgrade values (1, 700, 1200);insert into salgrade values (2, 1201, 1400);insert into salgrade values (3, 1401, 2000);insert into salgrade values (4, 2001, 3000);insert into salgrade values (5, 3001, 9999); insert into emp values (7369, 'SMITH', 'CLERK', 7902, '1980-12-17', 800, null, 20);insert into emp values (7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20', 1600, 300, 30);insert into emp values (7521, 'WARD', 'SALESMAN', 7698, '1981-02-22', 1250, 500, 30);insert into emp values (7566, 'JONES', 'MANAGER', 7839, '1981-04-02', 2975, null, 20);insert into emp values (7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28', 1250, 1400, 30);insert into emp values (7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01', 2850, null, 30);insert into emp values (7782, 'CLARK', 'MANAGER', 7839, '1981-06-09', 2450, null, 10);insert into emp values (7788, 'SCOTT', 'ANALYST', 7566, '1982-12-09', 3000, null, 20);insert into emp values (7839, 'KING', 'PRESIDENT', null, '1981-11-17', 5000, null, 10);insert into emp values (7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08', 1500, 0, 30);insert into emp values (7876, 'ADAMS', 'CLERK', 7788, '1983-01-12', 1100, null, 20);insert into emp values (7900, 'JAMES', 'CLERK', 7698, '1981-12-03', 950, null, 30);insert into emp values (7902, 'FORD', 'ANALYST', 7566, '1981-12-03', 3000, null, 20);insert into emp values (7934, 'MILLER', 'CLERK', 7782, '1982-01-23', 1300, null, 10);

1.模糊查询

? 1 2 3 4 mysql> select * from emp where ename like '%S%'; +-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job   | mgr | hiredate      | sal   | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+| 7369 | SMITH | CLERK  | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL |   20 || 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |   20 || 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |   20 || 7876 | ADAMS | CLERK  | 7788 | 1983-01-12 00:00:00 | 1100.00 | NULL |   20 || 7900 | JAMES | CLERK  | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL |   30 |+-------+-------+---------+------+---------------------+---------+------+--------+5 rows in set (0.00 sec) mysql> select * from emp where ename like 'S%'; +-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job   | mgr | hiredate      | sal   | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+| 7369 | SMITH | CLERK  | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL |   20 || 7788 | SCOTT | ANALYST | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |   20 |+-------+-------+---------+------+---------------------+---------+------+--------+2 rows in set (0.01 sec) mysql> select * from emp where ename like '%S';+-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job   | mgr | hiredate      | sal   | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+| 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |   20 || 7876 | ADAMS | CLERK  | 7788 | 1983-01-12 00:00:00 | 1100.00 | NULL |   20 || 7900 | JAMES | CLERK  | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL |   30 |+-------+-------+---------+------+---------------------+---------+------+--------+3 rows in set (0.00 sec) mysql> select * from emp where ename like '_O%';+-------+-------+---------+------+---------------------+---------+------+--------+| empno | ename | job   | mgr | hiredate      | sal   | comm | deptno |+-------+-------+---------+------+---------------------+---------+------+--------+| 7566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |   20 || 7902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL |   20 |+-------+-------+---------+------+---------------------+---------+------+--------+2 rows in set (0.00 sec)

总结：%表示任意0个或多个字符，可匹配任意类型和长度的字符；_表示任意单个字符，匹配单个任意字符。

2.排序

? 1 2 3 mysql> select * from emp order by sal;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename | job    | mgr | hiredate      | sal   | comm  | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+| 7369 | SMITH | CLERK   | 7902 | 1980-12-17 00:00:00 | 800.00 |  NULL |   20 || 7900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 | 950.00 |  NULL |   30 || 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 00:00:00 | 1100.00 |  NULL |   20 || 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 |   30 || 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |   30 || 7934 | MILLER | CLERK   | 7782 | 1982-01-23 00:00:00 | 1300.00 |  NULL |   10 || 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 |  0.00 |   30 || 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |   30 || 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 00:00:00 | 2450.00 |  NULL |   10 || 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 00:00:00 | 2850.00 |  NULL |   30 || 7566 | JONES | MANAGER  | 7839 | 1981-04-02 00:00:00 | 2975.00 |  NULL |   20 || 7788 | SCOTT | ANALYST  | 7566 | 1982-12-09 00:00:00 | 3000.00 |  NULL |   20 || 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 00:00:00 | 3000.00 |  NULL |   20 || 7839 | KING  | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |  NULL |   10 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec) mysql> select * from emp order by sal asc;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename | job    | mgr | hiredate      | sal   | comm  | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+| 7369 | SMITH | CLERK   | 7902 | 1980-12-17 00:00:00 | 800.00 |  NULL |   20 || 7900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 | 950.00 |  NULL |   30 || 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 00:00:00 | 1100.00 |  NULL |   20 || 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 |   30 || 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |   30 || 7934 | MILLER | CLERK   | 7782 | 1982-01-23 00:00:00 | 1300.00 |  NULL |   10 || 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 |  0.00 |   30 || 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |   30 || 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 00:00:00 | 2450.00 |  NULL |   10 || 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 00:00:00 | 2850.00 |  NULL |   30 || 7566 | JONES | MANAGER  | 7839 | 1981-04-02 00:00:00 | 2975.00 |  NULL |   20 || 7788 | SCOTT | ANALYST  | 7566 | 1982-12-09 00:00:00 | 3000.00 |  NULL |   20 || 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 00:00:00 | 3000.00 |  NULL |   20 || 7839 | KING  | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |  NULL |   10 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec) mysql> select * from emp order by sal desc;+-------+--------+-----------+------+---------------------+---------+---------+--------+| empno | ename | job    | mgr | hiredate      | sal   | comm  | deptno |+-------+--------+-----------+------+---------------------+---------+---------+--------+| 7839 | KING  | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |  NULL |   10 || 7788 | SCOTT | ANALYST  | 7566 | 1982-12-09 00:00:00 | 3000.00 |  NULL |   20 || 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 00:00:00 | 3000.00 |  NULL |   20 || 7566 | JONES | MANAGER  | 7839 | 1981-04-02 00:00:00 | 2975.00 |  NULL |   20 || 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 00:00:00 | 2850.00 |  NULL |   30 || 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 00:00:00 | 2450.00 |  NULL |   10 || 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |   30 || 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 |  0.00 |   30 || 7934 | MILLER | CLERK   | 7782 | 1982-01-23 00:00:00 | 1300.00 |  NULL |   10 || 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 |   30 || 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |   30 || 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 00:00:00 | 1100.00 |  NULL |   20 || 7900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 | 950.00 |  NULL |   30 || 7369 | SMITH | CLERK   | 7902 | 1980-12-17 00:00:00 | 800.00 |  NULL |   20 |+-------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec)

总结：order by排序默认按asc升序来排列也可指定desc降序排列

3.限制多少行

? 1 2 mysql> select * from emp limit 3;+-------+-------+----------+------+---------------------+---------+--------+--------+| empno | ename | job   | mgr | hiredate      | sal   | comm  | deptno |+-------+-------+----------+------+---------------------+---------+--------+--------+| 7369 | SMITH | CLERK  | 7902 | 1980-12-17 00:00:00 | 800.00 |  NULL |   20 || 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |   30 || 7521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 |   30 |+-------+-------+----------+------+---------------------+---------+--------+--------+3 rows in set (0.00 sec) mysql> select * from emp order by sal desc limit 3;+-------+-------+-----------+------+---------------------+---------+------+--------+| empno | ename | job    | mgr | hiredate      | sal   | comm | deptno |+-------+-------+-----------+------+---------------------+---------+------+--------+| 7839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL |   10 || 7902 | FORD | ANALYST  | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL |   20 || 7788 | SCOTT | ANALYST  | 7566 | 1982-12-09 00:00:00 | 3000.00 | NULL |   20 |+-------+-------+-----------+------+---------------------+---------+------+--------+3 rows in set (0.00 sec)

总结：limit限定显示前多少行，可与order by联合使用

4.聚合函

? 1 2 3 count() sum()函数用法：#1.各个部门的薪水和mysql> select deptno,sum(sal) from emp group by deptno;+--------+----------+| deptno | sum(sal) |+--------+----------+|   10 | 8750.00 ||   20 | 10875.00 ||   30 | 9400.00 |+--------+----------+3 rows in set (0.01 sec) #2.group by字段必须出现在select字段后面  各个部门的各个岗位的薪水和mysql> select deptno,job, sum(sal) from emp group by deptno ,job;+--------+-----------+----------+| deptno | job    | sum(sal) |+--------+-----------+----------+|   10 | CLERK   | 1300.00 ||   10 | MANAGER  | 2450.00 ||   10 | PRESIDENT | 5000.00 ||   20 | ANALYST  | 6000.00 ||   20 | CLERK   | 1900.00 ||   20 | MANAGER  | 2975.00 ||   30 | CLERK   |  950.00 ||   30 | MANAGER  | 2850.00 ||   30 | SALESMAN | 5600.00 |+--------+-----------+----------+9 rows in set (0.01 sec) #3.having  薪水和>5000的各个部门的各个岗位mysql> select deptno,job, sum(sal)   -> from emp   -> group by deptno ,job  -> having sum(sal)>5000; +--------+----------+----------+| deptno | job   | sum(sal) |+--------+----------+----------+|   20 | ANALYST | 6000.00 ||   30 | SALESMAN | 5600.00 |+--------+----------+----------+2 rows in set (0.00 sec)#4.常用组合where order limit select deptno,job, sum(sal) as sum_salfrom emp where job='SALESMAN'group by deptno ,jobhaving sum(sal)>5000 order by sum(sal) desc limit 1;

下面介绍下join及union的用法 数据准备：

? 1 2 3 4 5 create table testa(aid int,aname varchar(40)); create table testb(bid int,bname varchar(40),age int); insert into testa values(1,'xiaoming');insert into testa values(2,'LY');insert into testa values(3,'KUN');insert into testa values(4,'ZIDONG');insert into testa values(5,'HB');   insert into testb values(1,'xiaoming',10);insert into testb values(2,'LY',100);insert into testb values(3,'KUN',200);insert into testb values(4,'ZIDONG',110);insert into testb values(6,'niu',120);insert into testb values(7,'meng',130);insert into testb values(8,'mi',170);

5.left join

? 1 mysql> select  -> a.aid,a.aname,  -> b.bid,b.bname,b.age  -> from testa as a  -> left join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid | aname  | bid | bname  | age |+------+----------+------+----------+------+|  1 | xiaoming |  1 | xiaoming |  10 ||  2 | LY    |  2 | LY    | 100 ||  3 | KUN   |  3 | KUN   | 200 ||  4 | ZIDONG  |  4 | ZIDONG  | 110 ||  5 | HB    | NULL | NULL   | NULL |+------+----------+------+----------+------+5 rows in set (0.00 sec)

总结：a left join b  a表全，用b表去匹配a表LEFT JOIN 关键字会从左表 (a) 那里返回所有的行，即使在右表 (b) 中没有匹配的行,匹配不到的列用NULL代替

6.right join

? 1 mysql> select  -> a.aid,a.aname,  -> b.bid,b.bname,b.age  -> from testa as a  -> right join testb as b on a.aid=b.bid;+------+----------+------+----------+------+| aid | aname  | bid | bname  | age |+------+----------+------+----------+------+|  1 | xiaoming |  1 | xiaoming |  10 ||  2 | LY    |  2 | LY    | 100 ||  3 | KUN   |  3 | KUN   | 200 ||  4 | ZIDONG  |  4 | ZIDONG  | 110 || NULL | NULL   |  6 | niu   | 120 || NULL | NULL   |  7 | meng   | 130 || NULL | NULL   |  8 | mi    | 170 |+------+----------+------+----------+------+7 rows in set (0.00 sec)

总结：a right join b  b表全，用a表去匹配b表RIGHT JOIN 关键字会右表 (b) 那里返回所有的行，即使在左表 (a) 中没有匹配的行,匹配不到的列用NULL代替

7.inner join

? 1 2 mysql> select  -> a.aid,a.aname,  -> b.bid,b.bname,b.age  -> from testa as a  -> inner join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid | aname  | bid | bname  | age |+------+----------+------+----------+------+|  1 | xiaoming |  1 | xiaoming |  10 ||  2 | LY    |  2 | LY    | 100 ||  3 | KUN   |  3 | KUN   | 200 ||  4 | ZIDONG  |  4 | ZIDONG  | 110 |+------+----------+------+----------+------+4 rows in set (0.00 sec) mysql> select  -> a.aid,a.aname,  -> b.bid,b.bname,b.age  -> from testa as a  -> join testb as b on a.aid=b.bid; +------+----------+------+----------+------+| aid | aname  | bid | bname  | age |+------+----------+------+----------+------+|  1 | xiaoming |  1 | xiaoming |  10 ||  2 | LY    |  2 | LY    | 100 ||  3 | KUN   |  3 | KUN   | 200 ||  4 | ZIDONG  |  4 | ZIDONG  | 110 |+------+----------+------+----------+------+4 rows in set (0.00 sec)

总结：inner join 与join 效果一样在表中存在至少一个匹配时，INNER JOIN 关键字返回行

8.union与union all

? 1 2 mysql> select aid,aname from testa  -> union  -> select bid,bname from testb;+------+----------+| aid | aname  |+------+----------+|  1 | xiaoming ||  2 | LY    ||  3 | KUN   ||  4 | ZIDONG  ||  5 | HB    ||  6 | niu   ||  7 | meng   ||  8 | mi    |+------+----------+8 rows in set (0.01 sec) mysql> select aid,aname from testa  -> union all  -> select bid,bname from testb;+------+----------+| aid | aname  |+------+----------+|  1 | xiaoming ||  2 | LY    ||  3 | KUN   ||  4 | ZIDONG  ||  5 | HB    ||  1 | xiaoming ||  2 | LY    ||  3 | KUN   ||  4 | ZIDONG  ||  6 | niu   ||  7 | meng   ||  8 | mi    |+------+----------+12 rows in set (0.00 sec)

总结：union 会去重 union all不去重

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原文链接：https://cloud.tencent.com/developer/article/1500380